Solid oxide fuel cell having composition gradient between electrode and electrolyte

Abstract

A solid oxide fuel cell and method of making same is disclosed. An electrolyte layer of an oxide ion conductor material that may be specified by La1-aAaGa1-(b+c)BbCocO3 and an air electrode layer of an electron conductor material that may be specified by La1-dAdCoO3 are laminated, preferably with an intermediate layer of an electron and ion mixed conductor material that may be specified by La1-eAeGa1-(f+g)BfCogO3 interposed therebetween. The laminate may be sintered to integrate the layers, and may then subjected to a heat treatment to cause elements to diffuse through an interface between adjoining layers. The composition in each interface is thus continuously changed. Here, A may be at least one element selected from the group consisting of Sr and Ca, B may be at least one element selected from the group consisting of Mg, Al, and In, and 0.05<=a<=0.3, 0<=b, e<=0.3, 0<=c<=0.15, b+c<=0.3, 0<=d<=0.5, 0<=f<=0.15, 0.15<g<=0.3, and f+g<=0.3. The cell is free from cracks distortion, delamination, and the increase in interface resistance under thermal stress during sintering is reduced. In addition, an increase in the reaction area in an air electrode results in an improved cell efficiency.

What is claimed is:  
     
       1. A solid oxide fuel cell having a laminate structure, comprising: 
       an air electrode layer;  
       a fuel electrode layer;  
       a solid electrolyte layer interposed between said air electrode layer and said fuel electrode layer; and  
       an intermediate layer interposed between said electrolyte layer and said air electrode layer,  
       wherein said electrolyte layer comprises a perovskite type oxide ion conductor material, said air electrode layer comprises a perovskite type electron conductor material, and said intermediate layer comprises a perovskite type electron and ion mixed conductor material,  
       wherein a composition continuously changes in each of an interface between said intermediate layer and said electrolyte layer and an interface between said intermediate layer and said air electrode layer, and  
       wherein said electrolyte layer, said air electrode layer, and said intermediate layer comprise at least one common identical metal element.  
     
     
       2. The solid oxide fuel cell according to claim  1 , wherein said electrolyte layer comprises a material specified by La 1−a A a Ga 1−(b+c) B b Co c O 3 , and said air electrode layer comprises a material specified by La 1−d A d CoO 3 , and wherein A is at least one element selected from the group consisting of Sr and Ca and mixtures thereof, B is at least one element selected from the group consisting of Mg, Al and In and mixtures thereof, and 0.05≦a≦0.3, 0≦b≦0.3, 0≦c≦0.15, b+c≦0.3, and 0≦d≦0.5. 
     
     
       3. A solid oxide fuel cell having a laminate structure, comprising: 
       an air electrode layer;  
       a fuel electrode layer;  
       a solid electrolyte layer interposed between said air electrode layer and said fuel electrode layer; and  
       an intermediate layer interposed between said electrolyte layer and said air electrode layer;  
       wherein said electrolyte layer comprises a material specified by La 1−a A a Ga 1−(b+c) B b Co c O 3 , said air electrode layer comprises a material specified by La 1−d A d CoO 3 , and said intermediate layer comprises a material specified by La 1−e A e Ga 1−(f+g) B f Co g O 3 , and wherein A is at least one element selected from the group consisting of Sr and Ca, B is at least one element selected from the group consisting of Mg, Al, and In, and 0.05≦a≦0.3, 0≦b, e≦0.3, 0≦c≦0.15, b+c≦0.3, 0≦d≦0.5, 0≦f≦0.15, 0.15<g≦0.3, and f+g≦0.3;  
       and wherein a composition continuously changes in each of an interface between said intermediate layer and said electrolyte layer and an interface between said intermediate layer and said air electrode layer.  
     
     
       4. The solid oxide fuel cell according to claim  3 , wherein said electrolyte layer and said air electrode layer comprise at least one common identical metal element. 
     
     
       5. A method of manufacturing a solid oxide fuel cell, comprising the steps of: 
       laminating, into a laminate, an air electrode layer, at least one intermediate layer, and an electrolyte layer with said intermediate layer interposed between said air electrode layer and said electrolyte layer;  
       sintering said laminate to integrate said air electrode layer, said intermediate layer, and said electrode layer; and  
       heat treating said laminate for diffusing an element constituting said air electrode into said intermediate layer in the interface in the interface between said air electrode layer and said intermediate layer, or for diffusing an element constituting said intermediate layer into said air electrode layer in the interface therebetween, or for diffusing said element of said air electrode layer into said intermediate layer and said element of said intermediate layer into said air electrode layer in the interface therebetween, and for diffusing an element constituting said intermediate layer into said electrolyte layer in the interface between said intermediate layer and said electrolyte layer, or for diffusing an element constituting said electrolyte layer into said intermediate layer in the interface therebetween, or for diffusing said element of said intermediate layer into said electrolyte layer and said element of said electrolyte layer into said intermediate layer in the interface therebetween;  
       to produce a solid oxide fuel cell having a laminate structure, comprising:  
       an air electrode layer;  
       a fuel electrode layer;  
       a solid electrolyte layer interposed between said air electrode layer and said fuel electrode layer; and  
       an intermediate layer interposed between said electrolyte layer and said air electrode layer,  
       wherein said electrolyte layer comprises a perovskite type oxide ion conductor material, said air electrode layer comprises a perovskite type electron conductor material, and said intermediate layer comprises a perovskite type electron and ion mixed conductor material,  
       wherein a composition continuously changes in each of an interface between said intermediate layer and said electrolyte layer and an interface between said intermediate layer and said air electrode layer, and  
       wherein said electrolyte layer, said air electrode layer, and said intermediate layer comprise at least one common identical metal element.  
     
     
       6. The method of manufacturing a solid oxide fuel cell according to claim  5 , wherein said electrolyte layer comprises a material specified by La 1−a A a Ga 1−(b+c) B b Co c O 3 , said air electrode layer comprises a material specified by La 1−d A d CoO 3 , and wherein A is at least one element selected from the group consisting of Sr and Ca and mixtures thereof, B is at least one element selected from the group consisting of Mg, Al and In and mixtures thereof, and 0.05≦a≦0.3, 0≦b≦0.3, 0≦c≦0.15, b+c≦0.3, and 0≦d≦0.5. 
     
     
       7. The method of manufacturing a solid oxide fuel cell according to claim  5 , wherein the composition of said intermediate layer is intermediate between the composition of said electrolyte layer and the composition of said air electrode layer. 
     
     
       8. The method of manufacturing a solid oxide fuel cell according to claim  5 , wherein said electrolyte layer comprises a material specified by La 1−a A a Ga 1−(b+c) B b Co c O 3 , said air electrode layer comprises a material specified by La 1−d A d CoO 3 , and said intermediate layer comprises a material specified by La 1−e A e Ga 1−(f+g) B f Co g O 3 , and wherein A is at least one element selected from the group consisting of Sr and Ca and mixtures thereof, B is at least one element selected from the group consisting of Mg, Al and In and mixtures thereof, and 0.05≦a≦0.3, 0≦b, e≦0.3, 0≦c≦0.15, b+c≦0.3, 0≦d≦0.5, 0≦f≦0.15, 0.15<g≦0.3, and f+g≦0.3. 
     
     
       9. A method of manufacturing a solid oxide fuel cell, comprising the steps of: 
       laminating, into a laminate, an air electrode layer, at least one intermediate layer, and an electrolyte layer with said intermediate layer interposed between said air electrode layer and said electrolyte layer;  
       sintering said laminate to integrate said air electrode layer, said intermediate layer, and said electrode layer; and  
       heat treating said laminate for diffusing an element constituting said air electrode into said intermediate layer in the interface in the interface between said air electrode layer and said intermediate layer, or for diffusing an element constituting said intermediate layer into said air electrode layer in the interface therebetween, or for diffusing said element of said air electrode layer into said intermediate layer and said element of said intermediate layer into said air electrode layer in the interface therebetween, and for diffusing an element constituting said intermediate layer into said electrolyte layer in the interface between said intermediate layer and said electrolyte layer, or for diffusing an element constituting said electrolyte layer into said intermediate layer in the interface therebetween, or for diffusing said element of said intermediate layer into said electrolyte layer and said element of said electrolyte layer into said intermediate layer in the interface therebetween;  
       to produce a solid oxide fuel cell having a laminate structure, comprising:  
       an air electrode layer;  
       a fuel electrode layer;  
       a solid electrolyte layer interposed between said air electrode layer and said fuel electrode layer; and  
       an intermediate layer interposed between said electrolyte layer and said air electrode layer;  
       wherein said electrolyte layer comprises a material specified by La 1−a A a Ga 1−(b+c) B b Co c O 3 , said air electrode layer comprises a material specified by La 1−d A d CoO 3 , and said intermediate layer comprises a material specified by La 1−e A e Ga 1−(f+g) B f Co g O 3 , and wherein A is at least one element selected from the group consisting of Sr and Ca, B is at least one element selected from the group consisting of Mg, Al, and In, and 0.05≦a≦0.3, 0≦b, e≦0.3, 0≦c≦0.15, b+c≦0.3, 0≦d≦0.5, 0≦f≦0.15, 0.15<g≦0.3, and f+g≦0.3;  
       and wherein a composition continuously changes in each of an interface between said intermediate layer and said electrolyte layer and an interface between said intermediate layer and said air electrode layer.  
     
     
       10. The method of manufacturing a solid oxide fuel cell according to claim  9 , wherein said electrolyte layer and said air electrode layer comprise at least one common identical metal element. 
     
     
       11. The method of manufacturing a solid oxide fuel cell according to claim  9 , wherein said electrolyte layer, said air electrode layer and said intermediate layer, comprise at least one common identical metal element.